To fulfill requirements of speedup in mobile wireless communications, broadband wireless communications become essential. In broadband mobile wireless communications, influence of a plurality of delay paths causes frequency selective phasing to arise on a frequency axis, with which channel quality (or Channel Quality Indicator: CQI) varies. Moreover, when considering multiple access in which a base station communicates with a plurality of mobile stations (also referred to as User Equipments: UE's), the mobile stations communicate with the base station in different environments, so that CQI in the frequency domain is different from mobile station to mobile station. Thus, it has been known that system throughput is improved by making scheduling comprising comparing CQI in the frequency domain for a mobile station with each other, and allocating a sub-carrier with excellent CQI to each mobile station. Such scheduling is generally referred to as channel-dependent frequency scheduling or frequency domain channel-dependent scheduling.
According to Long Term Evolution (LTE) being currently standardized in the 3rd Generation Partnership Project (3GPP), Orthogonal Frequency Division Multiplexing (OFDM) is adopted for a downlink access scheme. The aforementioned channel-dependent frequency scheduling is applied to an LTE downlink, and a plurality of frequency blocks can be allocated per mobile station, where a frequency block is composed of resource blocks (each of which is composed of a plurality of sub-carriers) that are consecutive on the frequency axis within one transmit time Interval (TTI). FIG. 17 shows an example of frequency block allocation in an LTE downlink. This represents a case in which four mobile stations are scheduled within one TTI in a system band. The frequency block count for mobile station 1 (UE1) is three, the frequency block count for mobile station 2 (UE2) is two, the frequency block for mobile station 3 (UE3) counts two, and the frequency block for mobile station 4 (UE4) counts one.
On the other hand, for an access scheme in an LTE uplink, Single Carrier-Frequency Division Multiplexing Access (SC-FDMA) is adopted (which is also referred to as Discrete Fourier Transform-spread-OFDM (DFT-s-OFDM) in a transmitter configuration for sub-carrier mapping in the frequency domain.) In an LTE uplink, again, channel-dependent frequency scheduling is applied; however, to hold the Peak to Average Power Ratio (PAPR) down to a smaller value, a limit is placed in allocating consecutive resource blocks per mobile station within one TTI. This means that the frequency block count is always one. FIG. 18 shows an example of frequency block allocation in an LTE uplink. As with FIG. 17, this represents a case in which four mobile stations are scheduled within one TTI in a system band. The frequency block count for any one of mobile stations 1-4 (UE1-UE4) is always one.
Non-patent Document 1 has proposed contemplation of improvement of system throughput by adopting an access scheme (which will be sometimes referred to as Multi-Carrier FDMA (MC-FDMA) hereinbelow), which allows allocation of a plurality of frequency blocks per mobile station within one TTI, as an extended version of SC-FDMA, to enhance a multi-diversity effect in frequency scheduling. It should be noted that the Multi-Carrier FDMA (MC-FDMA) is a scheme sometimes referred to as FDMA-Adaptive Spectrum Allocation (FDMA-ASA).
FIG. 19 shows exemplary SC-FDMA and MC-FDMA transmitter configurations, and their spectra. The block configurations in the SC-FDMA and MC-FDMA transmitters are the same, which is comprised of a data generating section 1701, a DFT section 1702, a sub-carrier mapping section 1703, an IFFT (Inverse Fast Fourier Transform) section 1704, and a cyclic prefix section 1705.
First, data production is performed in the data generating section 1701, and signals in the time domain are transformed into those in the frequency domain at the DFT section 1702, which are then supplied to the sub-carrier mapping section 1703 as input. A difference between SC-FDMA and MC-FDMA is the limit of the frequency block count in mapping sub-carriers in the sub-carrier mapping section. While the frequency spectrum is always continuous in SC-FDMA (frequency block count=1), it may be discrete in MC-FDMA (frequency block count>1). Next, at the IFFT section 1704, the signals in the frequency domain is transformed into those in the time domain, which are then added with a cyclic prefix, and transmitted. Cyclic prefix addition refers to an operation of copying a tail of data to a head of a block, as shown in FIG. 20. The cyclic prefix is inserted for the purpose of effectively implementing frequency domain equalization on the receiver side. The length of the cyclic prefix is desirably set such that the maximum delay time of delay paths in the channel is not exceeded.
Moreover, PAPR in OFDM increases as the number of sub-carriers becomes larger. However, an increase of PAPR is significantly reduced for a number of sub-carriers of the order of 50, at which PAPR is almost saturated. In broadband transmission in which the multi-user diversity effect can be expected, the number of sub-carriers is usually greater than 50, in which case improvement of PAPR cannot be expected even with a smaller frequency block count. On the other hand, since in MC-FDMA, a frequency spectrum that is discrete on the frequency axis is introduced for a larger frequency block count, resulting in higher PAPR. Therefore, improvement of PAPR can be expected by holding the frequency block count down to a smaller value in MC-FDMA.
By increasing the frequency block count, the degree of freedom in allocating resource blocks becomes higher, and the multi-diversity effect in channel-dependent frequency scheduling is enhanced. However, when the frequency block count is increased, the overhead due to notification of information on resource block allocation may be greater. In fact, a bitmap method (a notification method suitable for a larger frequency block count), which is currently being studied for adoption in notification of information on resource block allocation in an LTE downlink (see Non-patent Documents 2, 3), has a greater overhead than that in a tree-based method (a notification method suitable for a smaller frequency'block count) for use in notification of information on resource block allocation in an LTE uplink (see Non-patent Document 4).
In particular, in a case that 100 resource blocks are to be allocated, 100-bit scheduling information is required in using the bitmap method, whereas log2 100 (100+1)/2=13-bit scheduling information is required using the tree-based method (for frequency block=1). In practice, in an LTE downlink, a limit is imposed on the resource blocks to be allocated such that a maximum of 37-bit of scheduling information is used. Moreover, when the tree-based method is applied to a case with a larger frequency block count, a required number of bits in notification is (frequency block count) times larger than that in SC-FDMA in which the frequency block count is one. In particular, assuming that the overhead in using the tree-based method for frequency block count=1 is 13 bit as described above, the overhead is increased such as 13×2=26 bits for frequency block count=2, or 13×4=52 bits for frequency block count=4.
Non-patent Document 1: “A Study on Broadband Single Carrier Transmission Technique using Dynamic Spectrum Control” by Keigo MASHIMA and Seiichi SAMPEI, Technical Report of IEICE, RCS2006-233, January 2007
Non-patent Document 2: 3GPP R1-074208, LG Electronics, “DL LVRB allocation approach 2,” October 2007
Non-patent Document 3: 3GPP R1-072723, Mitsubishi Electric, “Scheduling Policy and Signaling way on DL Resource Allocation,” June 2007
Non-patent Document 4: 3GPP R1-070881, NEC Group, NTT DoCoMo, “Uplink Resource Allocation for E-UTRA,” February 2007